1. Field of the Invention
The present invention relates to a valve operating system in an internal combustion engine, including an associative-operation switchover means which is provided between a plurality of rocker arms and includes a switchover pin provided astride between adjacent ones of the rocker arms and movable between an associatively operating position where the adjacent rocker arms are operated in association with each other and an associative-operation releasing position where the switchover pin is separated from one of the adjacent rocker arms to release the associative operation, one of the adjacent rocker arms being provided with first and second support walls with the second support wall disposed on the side of the other rocker arm, a roller disposed between the first and second support walls to come into rolling contact with a cam provided on a camshaft, and a cylindrical roller shaft provided between the first and second support walls with the roller rotatably carried thereon, so that the switchover pin can be slidably fitted into the roller shaft in response to the movement thereof to the associatively operating position.
2. Description of the Related Art
Such a valve operating system is conventionally known from Japanese Patent Application Laid-open No. 11-13440, for example.
In the above known valve operating system, a fixing pin is inserted and fixed in a rocker arm to engage an outer surface of a roller shaft fitted in a fitting bore provided in the rocker arm in order to fix a roller shaft to the rocker arm. For this reason, the fixing pin is required to fix the roller shaft, resulting in an increased number of parts, and it is necessary to conduct an operation of inserting and fixing the fixing pin, resulting in an increased number of assembling steps. Moreover, CD it is necessary to provide an insertion bore for insertion of the fixing pin in the rocker arm and to provide a groove for engagement of the fixing pin in the outer surface of the roller shaft, resulting in an increased number of processing steps.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a valve operating system in an internal combustion engine, wherein the roller shaft for supporting the roller thereon and guiding the switchover pin can easily be fixed to the rocker arm, while avoiding an increase in number of part and an increase in number of processing steps.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a valve operating system in an internal combustion engine, comprising an associative-operation switchover means which is provided between a plurality of rocker arms and includes a switchover pin provided astride between adjacent ones of the rocker arms and movable between an associatively operating position where the adjacent rocker arms are operated in association with each other and an associative-operation releasing position where the switchover pin is separated from one of the adjacent rocker arms to release the associative operation, one of the adjacent rocker arms being provided with first and second support walls with the second support wall disposed on the side of the other rocker arm, a roller disposed between the first and second support walls to come into rolling contact with a cam provided on a camshaft, and a cylindrical roller shaft provided between the a first and second support walls with the roller rotatably carried thereon, so that the switchover pin can be slidably fitted into the roller shaft in accordance with the movement thereof to the associatively operating position, wherein the roller shaft is press-fitted into at least second one of the first and second support walls, and a press-fit margin for the roller shaft press-fitted into the second support wall on the side of the other rocker arm is set smaller than a press-fit margin for the roller shaft press-fitted into the second support wall on the side of the roller.
With the arrangement of the first feature, the roller shaft is fixed to the rocker arm by press-fitting thereof into at least the second support wall. Therefore, as compared with the conventionally known system in which a fixing pin is required to fix the roller shaft, the roller shaft can be fixed easily to the rocker arm, while avoiding an increase in number of parts and an increase in number of processing steps. Moreover, during movement of the switchover pin to the associatively operating position, the deformation of an end of the roller shaft receiving the switchover pin due to the press-fitting can be suppressed to a small level, thereby smoothening the fitting of the switchover pin into the roller shaft to smoothen the switching-over between the associative operation of the adjacent rocker arms and the releasing of the associative operation by the switchover pin.
According to a second aspect and feature of the present invention, in addition to the first feature, the roller shaft is press-fitted into the first and second support walls with the press-fit margin in the first support wall being larger than the press-fit margin in the second support wall. With the arrangement of the second feature, during movement of the switchover pin to the associatively operating position, the deformation of the end of the roller shaft receiving the switchover pin, i.e., adjacent the second support wall due to the press-fitting can be suppressed to a small level, thereby smoothening the fitting of the switchover pin into the roller shaft to smoothen the switching-over between the associative operation of the adjacent rocker arms and the releasing of the associative operation by the switchover pin. Further, the press-fitting operation for the roller shaft can be facilitated by press-fitting the roller shaft from the outside of the second support wall.
According to a third aspect and feature of the present invention, in addition to the first feature, the press-fit margin for the roller shaft into the second support wall in that portion of a press-fit area which is on the side of the other rocker arm is set so as to be decreased gradually as being closer to the other rocker arm. With such arrangement, during movement of the switchover pin to the associatively operating position, the deformation of the end of the roller shaft receiving the switchover pin due to the press-fitting is decreased toward the other rocker arm. Thus, it is possible to further smoothen the fitting of the switchover pin into the roller shaft to further smoothen the switching-over between the associative operation of the adjacent rocker arms and the releasing of the associative operation by the switchover pin.
According to a fourth aspect and feature of the present invention, in addition to the first feature, the rocker arm is provided with a swinging support portion to which a base end of each of the first and second support walls is connected and which is swingably carried on an arm support portion provided in a cylinder head, and a recess is defined between the first and second support walls and located on the side of the camshaft, a portion of the cam in contact with the roller disposed at the central portion of the recess being accommodated in the recess. With such arrangement of the fifth feature, the camshaft can be disposed in proximity to the rocker arm in such a manner that a portion of the cam is accommodated in the recess on an upper surface of the rocker arm, thereby increasing the degree of freedom of the layout of the rocker arm and the camshaft to provide a reduction in size of the entire engine. Moreover, both of the support walls act as reinforcing ribs and thus, it is possible to enhance the rigidity of supporting of the swinging support portion on the arm support portion.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the recess is defined in an upper surface of the rocker arm, so that the oil can be accumulated in the recess and can be guided toward the roller. With such arrangement of the fifth feature, the oil can be accumulated in the recess in the upper surface of the rocker arm to lubricate the roller.
According to a sixth aspect and feature of the present invention, in addition to the first feature, a free rocker arm of the plurality of rocker arms disposed adjacent one another, which is freed relative to an engine valve when the associative-operation switchover means is brought into the associative-operation releasing state, is provided with a connection wall opposed to the roller and connecting the support walls to each other, the connection wall having a receiving portion provided thereon substantially in correspondence to the axially central portion of the roller to come into contact with an urging means for exhibiting a spring force for urging the free rocker arm toward the cam corresponding to the free rocker arm.
With such arrangement of the sixth feature, a point of a load applied from the cam to the free rocker arm and a point of an urging force applied from the urging means cannot be displaced largely in the axial direction of the roller, thereby enabling the stable swinging supporting of the free rocker arm. Moreover, the pair of support walls are interconnected by the connection wall and hence, the rigidity of supporting of the roller rotatably supported between the support walls can be enhanced.
According to a seventh aspect and feature of the present invention, in addition to the sixth feature, the connection wall is disposed below the roller and formed into such a shape that the distance between the connection wall and the roller is decreased toward the lowermost portion of the roller. With such arrangement of the seventh feature, the oil can be retained between the roller and the connection wall, and the lubrication of the roller can be performed by the oil.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.